msm_dcvs: Update interface to get updated timer on IDLE_EXIT

TZ DCVS algorithm is updated to give a new timer value on idle_exit
in order to catch smaller CPU bursts correctly. Also protect
against a timer race condition between IDLE_EXIT and CLOCK_FREQ_CHANGE
events.

Change-Id: I1ab414e9cd582c0eb8f86f0d87fa132d709da100
Signed-off-by: Eugene Seah <eseah@codeaurora.org>